A bigger question to ask is how much can she list and still operate her lifeboats? That was one of the issues with the Titanic so there is no excuse to not abandon ship before she reaches that point. It sounds like from some media reports some of the lifeboats did tip enough from scraping the sides to put people in the water.

The problems with the Titanic were many, there weren't enough lifeboats, there had been no lifeboat drill and no one knew what to do to abandon ship, and remember, the Titanic was "unsinkable".

Every new generation or two they have to learn the lesson again from the school of hard knocks.

Do passenger ship designs include watertight compartments to protect against severe flooding?

All modern ships have watertight compartments, some are better than others. The Titanic had around 6 watertight doors (I don't remember the exact number).

Unfortunately, they were not completely watertight in that they did not reach from deck to bulkhead.

As the bow went down, the fullly flooded compartments tipped over into the next & so on.

Since then, all watertight doors must be deck to bulkhead.

IIRC recently there was discussion in the news about that. The engineer was on-board and knew before sinking that the berg had put a hole through enough separate compartments that she would sink. IIRC she could take four being flooded, the hole got six.

Visits to the bridge are to be restricted and ships will have to carry more lifejackets under new cruise ship safety requirements agreed by the industry in the wake of the Costa Concordia disaster.

To be implemented with immediate effect, the measures also make it mandatory for all members of the bridge team to agree the ship’s course before the vessel sets sail. This was just a recommendation under current International Maritime Organisation rulings. The new requirement follows claims that Concordia’s Captain, Francesco Schettino deviated from the ship’s approved route to “salute” the residents on the island of Giglio.

Visits to the bridge are to be restricted and ships will have to carry more lifejackets under new cruise ship safety requirements agreed by the industry in the wake of the Costa Concordia disaster.

To be implemented with immediate effect, the measures also make it mandatory for all members of the bridge team to agree the ship’s course before the vessel sets sail. This was just a recommendation under current International Maritime Organisation rulings. The new requirement follows claims that Concordia’s Captain, Francesco Schettino deviated from the ship’s approved route to “salute” the residents on the island of Giglio.

The Italian Government has established that ships bigger ha 500 tons must stay away 2 km from isles and small harbors. The Liguria shopkeepers are protesting that in the deep Tyrrhenian Sea ships cannot drop anchors at that distance from the shore and send passengers ashore to spend their money by motorboats, while ships could anchor in the shallower Adriatic Sea. A compromise is likely to follow.
Tullio

What hasn't been mentioned is why the ship was so vulnerable to a hole in it's hull... Has nothing been learnt for ship design since the Titanic or Herald of Free Enterprise disasters?

Well... Car ferry design has been modified in a minor way to reduce the possibility of a very rapid capsize due to water sloshing across a car deck.

But what of passenger ships? How does the safety there compare to the extreme lengths taken to make airliners safe?

Two solutions come to mind that would have kept the Italian cruise ship afloat and upright despite huge holes below the waterline:

1: Watertight longitudinal bulkheads along with the more normal transverse bulkheads;

2: Gas powered rapid-set expanding foam to flood a water flooded area with buoyant foam that could also seal up any hole. There must also be two layers of mesh loosely fitted on the inner side of the hull that would stretch during the collision but act to hold the foam in place. The foam system could be made as part of the existing water fire suppression system pipework.

If ships were constructed to the same standards as aircraft the cost of a large cruse liner could be up to 10 times what it currently is. The fares needed to recoup such an outlay would be so prohibitive as to make the construction uneconomic in the first place. Consequently passenger ship construction is necessarily a trade off between acceptable safety and cost.

We have a world recession and the first thing that cash strapped people do is cut back on leisure activities. The cruise industry reacts by cutting corners to the bare minimum. Judging by the number of regular engine failures, or fires that have been happening, planned maintenance is being skipped. In the case of the Concordia we had a Maverick Captain with a history of showing off, yet allowed to command.